Problem: Simplify the following expression: $z = \dfrac{8a - 9}{8a} \div \dfrac{1}{4}$
Answer: Dividing by a number is the same as multiplying by its inverse. $z = \dfrac{8a - 9}{8a} \times \dfrac{4}{1}$ When multiplying fractions, we multiply the numerators and the denominators. $z = \dfrac{(8a - 9) \times 4} {(8a) \times 1}$ $z = \dfrac{32a - 36}{8a}$ Simplify: $z = \dfrac{8a - 9}{2a}$